Solar Energy Multiple Choice Questions on “Solar Dryer”.
1. What is solar dryer?
a) Use solar energy to dry substances
b) Use solar energy to evaporate water and collect it within the same closed system
c) Use solar energy to evaporate water and collect its condensate within the same closed system
d) Use solar energy to dry liquids
Answer: a
Clarification: Solar dryer are devices that use solar energy to dry substances. Devices that use solar energy to evaporate water and collect its condensate within the same closed system are called solar stills.
2. What is the most popular use of solar dryer?
a) Water
b) Food
c) Chemicals
d) Industrial substances
Answer: b
Clarification: Popularly, solar dryers are used to dry foods. If not the, it is one of the most common application of solar dryers. Since the question specifies most popular, food is the answer.
3. What are the two general types of solar dryers?
a) Direct and active
b) Indirect and passive
c) Direct and indirect
d) Box like and cone shaped
Answer: c
Clarification: The two general types of solar dryers are direct and indirect. Active and passive are types of solar stills. Box like and cone shaped are some of the basic configurations of solar stills.
4. What is the basic working principle of direct solar dryers?
a) Direct exposure of substance to fire
b) Direct use of sunlight to start a heater which is then used to dry the substance
c) Indirect exposure of substance to sunlight
d) Dehydrating the substance by directly exposing to sunlight
Answer: d
Clarification: The basic working principle of direct solar dryers is that they directly expose the substance to sunlight. By directly exposing the substance, they dehydrate the substance. A heater may or may not be used in a solar dryer.
5. Which of the following best indicates an example of direct solar dryer?
a) Drying wet clothes on wired lines
b) Using the dryer of a washing machine
c) Using an electric heater
d) Using a solar heater
Answer: a
Clarification: Drying wet clothes on wired lines is an example of direct solar dryer. Many countries including India still use this traditional method to dry clothes as it is cheap and natural. Electric and solar heaters are not solar dryers.
6. How do wet clothes laid on wired lines dry under sunlight?
a) Wind blows to accumulate more air consisting moisture near the clothes
b) Wind blows away the moisture near the wet clothes air exposing them to fresh air and sunlight
c) Sunlight continuously evaporates water in wet clothes without any assistance from wind
d) Wind blows away the moisture near the wet clothes air exposing them to fresh air
Answer: b
Clarification: Both sunlight and wind assist drying of wet clothes laid on wired lines. As the sun evaporates water from the clothes, moisture content in the surrounding air increases. Wind blows away this moisture saturated air and exposes to the clothes to fresh air and sunlight. The process repeats thereby drying the wet clothes over time.
7. Which of the following surface is best suited to absorb sunlight?
a) White surface
b) Red surface
c) Black surface
d) Silver surface
Answer: c
Clarification: A black surface or a black coated surface is best suited to absorb sunlight. This is supported by the concept of black body. A black body is an idealized physical body that absorbs all incident electromagnetic radiation.
8. How does an indirect solar dryer work?
a) By directly exposing the substance to sunlight
b) By using an electrical heater
c) By heating the incoming air with the help of a black surface
d) By using fire
Answer: d
Clarification: An indirect solar dyer heats the incoming air with the help of a black surface. Then this heated air is passed over the substance to be dried thereby drying the substance.
9. Why is direct solar dryer harmful for food?
a) Because direct sunlight could chemically alter some food items
b) Because direct sunlight dries the food
c) Because direct solar dryer does not cover the food
d) Because of contaminants brought by wind
Answer: a
Clarification: A major problem with a direct solar dryer is that it can harm the food. This is because the sunlight could chemically alter some food item and make them less appetizing. Contamination due to wind is also a problem but it is not as bad as chemical alteration.
10. Indirect solar dryers protect the food.
a) False
b) True
Answer: b
Clarification: Indirect solar dryers protect the food from directly exposing it to sunlight. Since they heat the incoming air they do not directly expose the food to sunlight. This prevents chemical alteration of food items.
11. _______ are used as air exhausts in indirect solar dryers.
a) Turbines
b) Ceiling fans
c) Chimneys
d) Table fans
Answer: c
Clarification: Chimneys are used as air exhausts in indirect solar dryers. They let the moisture containing air pass out of the chamber thereby making room for freshly heated air.
12. A glass cover _______ solar dryers.
a) decreases the efficiency of
b) is not used in
c) does not affect the efficiency of
d) increases the efficiency of
Answer: d
Clarification: A glass cover increases the efficiency of solar dryers. Sometimes, direct solar dryers are equipped with glass covers to trap more heat thereby increasing the efficiency of the system.
13. Which of the following best explains the increment in efficiency of a glass covered solar dryer?
a) Greenhouse effect
b) Greenhouse gas
c) Climate change
d) Thermohaline circulation
Answer: a
Clarification: Greenhouse effect best explains the increment in efficiency of a glass covered solar dryer. Greenhouse effect is the process of increasing the temperature of a chamber covered with glass by trapping sun’s heat within the chamber.
14. Which of the following is an example of indirect solar dryer?
a) Wet clothes laid on wired lines
b) Solar cabinet dryer
c) Solar tunnel dryer
d) Biomass cabinet dryer
Answer: b
Clarification: Solar cabinet dryer is an example of indirect solar dryer. Wet clothes laid on wired lines is an example of direct solar dryer. Solar tunnel dryer and biomass cabinet dryer are not examples of indirect solar dryers.
15. Indirect solar dryers work on natural air convection.
a) True
b) False
Answer: a
Clarification: Indirect solar dryers work on natural air convection. This is because the incoming air is heated by a black surface. As the air is heated, it rises thereby giving room for the heavier colder air to get heated.